Equipment used in hydrocarbon exploration and production activities, such as steel tubulars and valves, often becomes contaminated with scale formed by the deposition of dissolved mineral salts. The problem is particularly acute in more mature oilfields where water injection is used to sustain reservoir pressure. Although the scale primarily comprises carbonates and sulphates, particularly barium sulphate (Barytes), quantities of naturally occurring radioactivity are present in the scale, in the form of Radium.sup.228 and Actinium.sup.226 and their daughters.
When scale contaminated components are taken out of use the radioactive scale is removed before disposal, for example, in the United Kingdom the requirements of the Radioactive Substances Act 1960 having to be met. At present the scale is removed by high pressure water jetting. This is a difficult and awkward procedure, as the scale builds up on interior surfaces and gaining entry to the interior of, for example, a valve body can be particularly difficult. Further, the scale which is removed is subject to handling and disposal restrictions. scale, typically, has an activity level of around 50 Bq/g (Becquerels per gram). Currently, in the United Kingdom, the scale removed from the components is either discharged into the sea or is treated and concentrated for long term safe storage. Increasingly stringent environmental controls limit, and may eventually prohibit, the disposal of such scale by discharging into the sea, and long term safe storage is expensive and likely to be unpopular with local residents and authorities.
A method of decontaminating radioactively contaminated scrap iron and/or steel is described in UK Patent Application No. 2 141 866 A. The method is concerned with the decontamination of material which is contaminated radioactively on the surface, such as is obtained from nuclear fuel reprocessing plants. The iron or steel is smelted in the presence of slagging agents, inactive isotopes of the radioactive elements present in the melt being added and subjected to the smelting process. It is said that the radioactive isotopes of the elements are driven out of the melt and are collected in the slag, resulting in a steel melt having a practically negligible radioactivity. The resulting radioactive slag is processed into refuse packs and which may be held in containers produced from the decontaminated iron or steel.
A further method of decontaminating molten steel is disclosed in Japanese Patent Application No. JP 1172508.